safeLogger

Crash-resistant SD log file creation library for Arduino

The Problem

I want to log data to an SD card on an Arduino. What happens if the Arduino resets, or my log file already exists? Do I overwrite? How do I create a new filename? Does appending to the previous filename make sense?

I don't want to risk file overwrites or lost data, and I didn't want to deal with weird timestamps in my datafiles, so I created this library.

Quickstart

Clone this repo into your Arduino project, and then include it with #include "safeLogger/safeLogger.h". Determine a basename and suffix for your logfile, e.g. "log" and "csv". Then you can get the "safe" filename using getLogName(&dir, "data", "csv");

Requirements

• "SD.h", which should come pre-installed in the Arduino IDE.

Code Snippet

This creates a logfile in the "root" of the SD card.

#include "SD.h"
#include "safeLogger/safeLogger.h"
int SD_CS = 4;
String fn;
char fnbase[] = "data";
char fnsfx[] = "csv";

void setup() {
    Serial.begin(115200);
    while (!SD.begin(SD_CS)) {
        Serial.println(F("SD card error"));
        delay(300);
    }
    File root = SD.open(F("/"));
    if (!root) {
        Serial.println(F("Error opening root"));
    }
    fn = getLogName(&root, fnbase, fnsfx);
    root.close();
    File logFile = SD.open(fn, FILE_WRITE);
    if (logFile) {
      logFile.println(F("I am a file"));
      logFile.close();
    } else {
        Serial.println(F("Logfile error"));
    }
}

How it Works

For a file suffix (e.g. "csv") and a basename (e.g. "data"), it will find all the files named "data.csv", then return a filename "data<max(digits)+1>.csv". This file is guaranteed to not exist and preserves sensible filename ordering.

Now everytime my Arduino resets, it creates a new file with digits+1, and I know if/when it reset and don't lose any data in the process, all while keeping my datafiles nice and ordered.